1. Field
The invention relates to implantable medical device systems, and more particularly to implantable medical device systems having the ability to communicate with devices outside of a patient for programming, interrogation, data retrieval, and other purposes.
2. Background
Epilepsy, a neurological disorder characterized by the occurrence of seizures (specifically episodic impairment or loss of consciousness, abnormal motor phenomena, psychic or sensory disturbances, or the perturbation of the autonomic nervous system), is debilitating to a great number of people. It is believed that as many as two to four million Americans may suffer from various forms of epilepsy. Research has found that its prevalence may be even greater worldwide, particularly in less economically developed nations, suggesting that the worldwide figure for epilepsy sufferers may be in excess of one hundred million.
Because epilepsy is characterized by seizures, its sufferers are frequently limited in the kinds of activities they may participate in. Epilepsy can prevent people from driving, working, or otherwise participating in much of what society has to offer. Some epilepsy sufferers have serious seizures so frequently that they are effectively incapacitated.
Furthermore, epilepsy is often progressive and can be associated with degenerative disorders and conditions. Over time, epileptic seizures often become more frequent and more serious, and in particularly severe cases, are likely to lead to deterioration of other brain functions (including cognitive function) as well as physical impairments.
The current state of the art in treating neurological disorders, particularly epilepsy, typically involves drug therapy and surgery. The first approach is usually drug therapy.
A number of drugs are approved and available for treating epilepsy, such as sodium valproate, phenobarbital/primidone, ethosuximide, gabapentin, phenytoin, and carbamazepine, as well as a number of others. Unfortunately, those drugs typically have serious side effects, especially toxicity, and it is extremely important in most cases to maintain a precise therapeutic serum level to avoid breakthrough seizures (if the dosage is too low) or toxic effects (if the dosage is too high). The need for patient discipline is high, especially when a patient's drug regimen causes unpleasant side effects the patient may wish to avoid.
Moreover, while many patients respond well to drug therapy alone, a significant number (at least 20-30%) do not. For those patients, surgery is presently the best-established and most viable alternative course of treatment.
Currently practiced surgical approaches include radical surgical resection such as hemispherectomy, corticectomy, lobectomy and partial lobectomy, and less-radical lesionectomy, transection, and stereotactic ablation. Besides being less than fully successful, these surgical approaches generally have a high risk of complications, and can often result in damage to eloquent (i.e., functionally important) brain regions and the consequent long-term impairment of various cognitive and other neurological functions. Furthermore, for a variety of reasons, such surgical treatments are contraindicated in a substantial number of patients. And unfortunately, even after radical brain surgery, many epilepsy patients are still not seizure-free.
Electrical stimulation is an emerging therapy for treating epilepsy. However, currently approved and available electrical stimulation devices apply continuous electrical stimulation to neural tissue surrounding or near implanted electrodes, and do not perform any detection—they are not responsive to relevant neurological conditions.
The NeuroCybernetic Prosthesis (NCP) from Cyberonics, for example, applies continuous electrical stimulation to the patient's vagus nerve. This approach has been found to reduce seizures by about 50% in about 50% of patients. Unfortunately, a much greater reduction in the incidence of seizures is needed to provide clinical benefit. The Activa device from Medtronic is a pectorally implanted continuous deep brain stimulator intended primarily to treat Parkinson's disease. In operation, it supplies a continuous electrical pulse stream to a selected deep brain structure where an electrode has been implanted.
Continuous stimulation of deep brain structures for the treatment of epilepsy has not met with consistent success. To be effective in terminating seizures, it is believed that one effective site where stimulation should be performed is near the focus of the epileptogenic region. The focus is often in the neocortex, where continuous stimulation may cause significant neurological deficit with clinical symptoms including loss of speech, sensory disorders, or involuntary motion. Accordingly, research has been directed toward automatic responsive epilepsy treatment based on a detection of imminent seizure.
A typical epilepsy patient experiences episodic attacks or seizures, which are generally electrographically defined as periods of abnormal neurological activity. As is traditional in the art, such periods shall be referred to herein as “ictal.”
Most prior work on the detection and responsive treatment of seizures via electrical stimulation has focused on analysis of electroencephalogram (EEG) and electrocorticogram (ECoG) waveforms. In general, EEG signals represent aggregate neuronal activity potentials detectable via electrodes applied to a patient's scalp. ECoG signals, deep-brain counterparts to EEG signals, are detectable via electrodes implanted on or under the dura mater, and usually within the patient's brain. Unless the context clearly and expressly indicates otherwise, the term “EEG” shall be used generically herein to refer to both EEG and ECoG signals.
As is well known, it has been suggested that it is possible to treat and terminate seizures by applying electrical stimulation to the brain. See, e.g., U.S. Pat. No. 6,016,449 to Fischell et al., and H. R. Wagner, et al., “Suppression of cortical epileptiform activity by generalized and localized ECoG desynchronization,” Electroencephalogr. Clin. Neurophysiol, 1975; 39(5): 499-506. And as stated above, it is believed to be beneficial to perform this stimulation only when a seizure (or other undesired neurological event) is occurring or about to occur, as inappropriate stimulation may result in the initiation of seizures.
It is especially beneficial to be able to tailor the operation of a neurostimulator (i.e., a device, preferably implantable, that delivers responsive electrical stimulation therapy as described above) to the specific needs of the patient. Accordingly, many neurostimulators and other implantable medical devices available and in development (in particular cardiac devices, such as pacemakers and implantable cardioverter-defibrillators, or ICDs) are programmable to some extent. Typically, however, programming and interrogation are performed with an expensive custom piece of equipment kept by the patient's hospital or clinic. To the extent a handheld or portable programmer is available to a patient, it is generally a standalone unit provided with a limited number of features and functions to avoid undesirable interference with the implantable device's clinical objectives.
With traditional solutions, device interrogation and programming can generally only be accomplished locally, i.e., in close proximity to the device being interrogated or programmed. Programmers and handheld control devices are relatively commonplace, but generally are not very sophisticated. Handheld devices are generally restricted to controlling a relatively small number of device parameters. Even other types of programmers typically are not sophisticated enough to be tied into multiple other devices or to have any ability to update or examine a patient's comprehensive treatment history, especially if the patient has not used that programmer before. Interaction with implantable medical devices has traditionally been limited by geographical considerations in the past.
It will be appreciated that it is desirable to have improved flexibility in managing patient care by enabling remote interrogation, programming, and interaction with implanted medical devices.
Modern implantable medical devices, such as neurostimulators, pacemakers, and ICDs, are capable of not only monitoring patient condition and delivering therapy, but also can store detailed data and diagnostics relating to a patient's condition for later retrieval. Analysis of this data can improve patient care dramatically, and allow fine-tuning the performance of the implantable devices by programming them with new operational parameters. Interrogation of an implantable medical device allows data stored in the device to be retrieved by an external device (which, presumably, is better equipped to analyze the data in great detail). After analysis, reprogramming the device allows its performance to be optimized based on the interrogated data.
In addition to the clinical utility provided by flexible interrogation and programming capabilities as described above, it is also desirable to be able to provide additional communications features to keep patients involved, informed, and invested in their own care. Traditional implantable medical devices, even those using programmers or hand-held control devices, are not well suited for this. Long-term care of epilepsy and cardiac patients, among others, requires a serious commitment from not only medical and clinical personnel, but also from patients. As described above, anti-epileptic drugs often have unpleasant side effects, so patients taking them should be made to feel like they have the information and control they need to effectively manage their disease, or they may become complacent and non-compliant. The same is true for patients with implantable medical devices—there is a danger that patients will take their devices for granted unless they are sufficiently involved.
Finally, it should be recognized that several tasks involved in the long-term care and management of neurological and cardiac patients are either labor-intensive or require inconvenient periodic office (or hospital) visits, even when the patient is being managed very well. It would be desirable to provide a mechanism for remote welfare-checks on patients with implantable devices, to allow their progress to be checked and data analyzed without the need for frequent office visits. Such a capability would preferably allow the user to store logs and notes regarding his or her condition, and would also facilitate the remote administration of examinations or surveys, as desired by the patient's treating medical team or physician.
Several others have attempted to leverage modern communications capabilities in the context of an implantable medical device system.
Medtronic, Inc. has tested an implantable diagnostic monitor for use in treating high-risk cardiac patients. See D. Sherman, “High-Tech Heart Devices Deliver Data Over the Web,” Reuters News Service (Aug. 8, 2001). However, the Medtronic devices used in the “Chronicle Study” appear to be monitors only and do not appear to provide therapy. It would be preferable to have a device that is not only a continuous monitor, but is also a closed-loop treatment system that can be programmed and optimized with information obtained via the monitoring function.
Medtronic also has available a programmable implantable pulse generator for treating neurological disorders, particularly tremor. The “Activa” device has several programmable settings, but is not enabled for diagnostic data storage and upload, and generally provides only continuous (or semi-continuous) pulse streams, not closed-loop therapy responsive to the detection of a relevant event. It is not adapted for remote control or administration.
Another company has developed a PDA-based system for monitoring patient status. See “MedSearch Technologies, Inc. Develops a Revolutionary Home-Care Wireless Technology Using PDAs—Personal Organizers—as Patient Monitors,” Business Wire (Sep. 25, 2000). However, the MedSearch system uses disposable sensors, and does not appear to tie into an implantable device system. Although a system such as the one from MedSearch might provide some additional convenience in the form of reduced office visits, it is not directly involved in a closed-loop treatment system and hence would not facilitate comprehensive remote patient care and management, only monitoring.
St. Jude Medical, Inc. developed the Housecall trans-telephonic data link system for implantable cardiac care devices. This device enabled the transmission of stored data and diagnostics from the implantable device to a remote location. However, the apparatus was relatively cumbersome, and it took a relatively long time to complete a single session of data transmission, leading to patient non-compliance. Like the systems described above, the Housecall system was intended to provide a remote monitoring function only, and did not serve as part of a closed-loop treatment system providing remote patient care.
Cyberonics, Inc. markets an implantable device for treating epilepsy; it is now also being tested for treating other disorders. The Cyberonics “NCP” (Neurocybemetic Prosthesis) is, in essence, an implantable pulse generator adapted, in this case, to apply electrical stimulation to the patient's vagus nerve. Like the Medtronic Activa, it applies a continuous or semi-continuous pulse stream, and only a few basic settings are programmable. It is not adapted to collect data or to provide responsive therapy, and no integrated system for network communications is available.
Clearly, an interactive implantable medical device system with enhanced network communications capabilities, geographic independence, and closed-loop treatment functionality would be desirable as it would greatly improve patient care and management for numerous diseases and disorders now treated with implantable devices that have only limited communications capabilities.